U.S. patent application number 10/261627 was filed with the patent office on 2003-04-10 for control system for engine.
Invention is credited to Kinugawa, Masumi, Kuboshima, Tsukasa, Saito, Makoto, Sekiguchi, Kiyonori, Yahata, Shigeto.
Application Number | 20030066510 10/261627 |
Document ID | / |
Family ID | 26623754 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030066510 |
Kind Code |
A1 |
Kuboshima, Tsukasa ; et
al. |
April 10, 2003 |
CONTROL SYSTEM FOR ENGINE
Abstract
The engine control system has an ECU that supplies relatively
large amount of EGR gas and delays an injection timing in order to
decrease temperature in a combustion chamber. When an engine is
operated under a warming up operation or a low engine load, the ECU
deactivates an EGR cooler to increase intake air temperature in
order to stabilize engine operation. When the engine is operated
under a high engine load, the ECU activates the EGR cooler, delays
a closing timing of an intake valve, and increases a boost pressure
of a forced induction system. As a result, both of a compression
end temperature and a maximum combustion temperature are decreased
so that emissions of NOx and particulates are reduced.
Inventors: |
Kuboshima, Tsukasa;
(Okazaki-City, JP) ; Sekiguchi, Kiyonori;
(Okazaki-City, JP) ; Kinugawa, Masumi;
(Okazaki-City, JP) ; Saito, Makoto; (Okazaki-City,
JP) ; Yahata, Shigeto; (Kariya-City, JP) |
Correspondence
Address: |
Larry S. Nixon, Esq.
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Rd.
Arlington
VA
22201-4714
US
|
Family ID: |
26623754 |
Appl. No.: |
10/261627 |
Filed: |
October 2, 2002 |
Current U.S.
Class: |
123/305 ;
123/316; 123/568.12 |
Current CPC
Class: |
F02M 26/10 20160201;
F02M 26/33 20160201; Y02T 10/47 20130101; Y02T 10/40 20130101; F02D
35/025 20130101; F02B 29/0406 20130101; F02D 15/00 20130101; Y02T
10/44 20130101; F02D 41/1446 20130101; F02D 41/086 20130101; F02D
2250/36 20130101; F02D 41/0065 20130101; F02M 26/28 20160201; F02D
41/401 20130101; F02M 26/05 20160201; F02D 2041/0067 20130101 |
Class at
Publication: |
123/305 ;
123/316; 123/568.12 |
International
Class: |
F02B 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2001 |
JP |
2001-309846 |
Jul 11, 2002 |
JP |
2002-202579 |
Claims
What is claimed is:
1. A control system for an engine, the system comprising: engine
load determining means for determining engine load; compression
ratio decreasing means for decreasing an actual compression ratio
from a theoretical compression ratio when the engine load is higher
than a predetermined level; and intake air increasing means for
increasing an amount of intake air induced into a combustion
chamber of the engine when the actual compression ratio is
decreased by the actual compression ratio decreasing means.
2. The control system for an engine according to claim 1, wherein
the engine has a variable intake valve timing device and a forced
induction device, the actual compression ratio decreasing means
delays a closing timing of an intake valve of the engine by
controlling the variable intake valve timing device, and the intake
air increasing means increases a boost pressure of the forced
induction device by controlling the forced induction device.
3. The control system for an engine according to claim 1, wherein
the engine load determining means includes a sensor for detecting
an operated position of an accelerator pedal.
4. The control system for an engine according to claim 1, wherein
the engine has a fuel injection system for injecting fuel directly
into the combustion chamber.
5. The control system for an engine according to claim 4, further
comprising: delayed injection means for injecting fuel into the
combustion chamber at a relatively delayed timing when the engine
load is in a low engine load range.
6. The control system for an engine according to claim 1, further
comprising: delayed ignition means for igniting fuel in the
combustion chamber at a relatively delayed timing when the engine
load is in a low engine load range.
7. The control system for an engine according to claim 1, further
comprising: EGR means for executing an exhaust-gas
recirculation.
8. The control system for an engine according to claim 7, further
comprising an EGR cooler for cooling an EGR gas, and EGR cooler
control means for activating the EGR cooler when the engine load is
higher than the predetermined level, and for deactivating the EGR
cooler when the engine load is in a low engine load range.
9. The control system for an engine according to claim 1, further
comprising: intake air temperature control means for decreasing
temperature of the intake air as the engine load is increased.
10. The control system for an engine according to claim 1, further
comprising: warming up control means for inhibiting the compression
ratio decreasing means and the intake air increasing means when the
engine is in a warming up operation.
11. The control system for an engine according to claim 1, wherein
the engine has a variable intake valve timing device and a forced
induction device, the engine load determining means includes means
for detecting an operated position of an accelerator pedal, and
determines whether the engine load is in a low engine load range, a
medium engine load range or a high engine load range corresponding
to a range higher than the predetermined level, the actual
compression ratio decreasing means delays a closing timing of an
intake valve of the engine by controlling the variable intake valve
timing device, and the intake air increasing means increases a
boost pressure of the forced induction device by controlling the
forced induction device, the increased boost pressure being higher
than that set before the actual compression ratio is decreased.
12. The control system for an engine according to claim 11, further
comprising: EGR device that returns a part of exhaust gas to an
intake side of the engine; EGR cooler that cools the exhaust gas
returning to the intake side via the EGR device; temperature
detecting means for detecting temperature of cooling water for
cooling the engine; and EGR cooler controlling means for
controlling the EGR cooler in an activated condition or a
deactivated condition based on the temperature detected by the
temperature detecting means and the engine load determined by the
engine load determining means.
13. The control system for an engine according to claim 12, wherein
the EGR cooler controlling means deactivates the EGR cooler when
the engine load is in the low engine load range or when the
temperature is lower than a predetermined temperature.
14. The control system for an engine according to claim 12, wherein
the EGR cooler controlling means activates the EGR cooler when the
engine load is in the medium or high engine load range.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Applications
No. 2001-309846 filed on Oct. 5, 2001 and No. 2002-202579 filed on
Jul. 11, 2002 the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a control system for an
internal combustion engine (engine).
[0004] 2. Description of Related Art
[0005] It is preferable to decrease a maximum combustion
temperature of fuel in a combustion chamber in order to reduce
emissions of nitrogen oxides (NOx) and particulates.
Conventionally, increasing an amount of exhaust-gas recirculation,
or delaying fuel injection is carried out to decrease the
temperature in the combustion chamber. However, the temperature in
the combustion chamber is still increased in a high engine load
condition according to the conventional measures.
[0006] JP-A-11-315739 discloses a combination of low compression
ratio engine and an engine control apparatus. According to
JP-A-11-315739, the engine having a relatively low theoretical
compression ratio can decrease a compression end temperature. The
theoretical compression ratio is determined geometrically based on
the engine dimensions. The compression end temperature is a
temperature in the combustion chamber just before beginning
combustion.
[0007] However, the temperature in the combustion chamber is
originally low during the engine starting and a low engine load
condition. Therefore, decreasing the theoretical compression ratio
may cause an instable ignition of fuel and make it difficult to
operate the engine stably. In order to avoid such disadvantages,
JP-A-11-315739 discloses the engine control apparatus that advances
a fuel injection timing and advances closing timing of intake
valves so that the compression end temperature is maintained above
a predetermined temperature. Advanced closing of the intake valves
increases an actual compression ratio since it decreases a back
flow of intake air. The actual compression ratio may be referred to
as an effective compression ratio. Advanced fuel injection timing
allows a fuel injection when a compressed air in the combustion
chamber still keeps a high temperature, and provides a relatively
stable ignition and combustion. According to the JP-A-11-315739, it
is possible to reduce the emissions in a medium engine load and to
keep combustions stable in a low engine load.
[0008] In case of an internal combustion engine for a vehicle the
engine is regularly used under the low engine load condition such
as a driving in a city. In such a low engine load conditions, the
advanced closing of the intake valve or the advanced fuel injection
may cause an excess increase of combustion temperature and cause an
increase of the emissions.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
control system for an engine that is capable of operating the
engine stably and reducing emissions of NOx and particulates.
[0010] It is another object of the present invention to operating
the engine stably and reducing the emissions without decreasing the
theoretical compression ratio.
[0011] According to an embodiment of the present invention, it is
possible to decrease temperature in a combustion chamber of the
engine. During the high engine load, heat generated in the
combustion chamber is increased due to an increase of fuel
injection amount. When the engine is operated under a high engine
load, an actual compression ratio is decreased. For example, a
closing timing of an intake valve of the engine is delayed.
However, decreasing the actual compression ratio may cause a
decrease of heat capacity in the combustion chamber, and cause an
increase of a maximum combustion temperature. In order to avoid
such disadvantage, an amount of intake air induced into the
combustion chamber is increased. For example, a boost pressure of a
forced induction system is increased. The increased boost pressure
is set higher than a boost pressure set before the actual
compression ratio is decreased. As a result, it is possible to
prevent decreasing of the heat capacity, and to decrease the
maximum combustion temperature. Therefore, it is possible to reduce
the emissions of NOx and particulates. Further, such advantages can
be achieved without decreasing a theoretical compression ratio.
[0012] Further, an EGR cooler may be controlled in accordance with
the engine load. For example, the EGR cooler is deactivated when
the engine load is in a low engine load range in order to increase
temperature of the intake air. Therefore, it is possible to improve
stability of the engine in the low engine load. The EGR cooler may
be deactivated when the engine is in a warming up operation.
[0013] Further, the present invention is effective for an engine
that is operated under a relatively large amount of EGR and a
relatively delayed injection timing. It is possible to enhance
reduction of the emissions of NOx and particulates, and to provide
a stable operation of the engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Features and advantages of embodiments will be appreciated,
as well as methods of operation and the function of the related
parts, from a study of the following detailed description, the
appended claims, and the drawings, all of which form a part of this
application. In the drawings:
[0015] FIG. 1 is a schematic diagram of an engine for a vehicle
according to a first embodiment of the present invention;
[0016] FIG. 2 is a block diagram of a control system for the engine
shown in FIG. 1 according to the first embodiment of the present
invention;
[0017] FIG. 3 is a flowchart showing an operation of the control
system according to the first embodiment of the present
invention;
[0018] FIG. 4 is a graph showing a relationship between an engine
speed and an output torque of the engine according to the first
embodiment of the present invention;
[0019] FIG. 5 is a graph showing a relationship between a crank
angle and a temperature in the cylinder (combustion chamber)
wherein a thick solid line indicates the first embodiment, a chain
line indicates an ordinary engine, a broken line indicates an
engine under a conventional control, and a narrow solid line
indicates an engine having low theoretical compression ratio;
[0020] FIG. 6 is a graph showing a relationship between a crank
angle and a temperature in the cylinder wherein a thick solid line
indicates the first embodiment, a chain line indicates an ordinary
engine, and a broken line indicates an engine under a conventional
control; and
[0021] FIG. 7 is a graph showing a relationship between an engine
load and a boost pressure wherein a broken line indicates a
conventional control and a solid line indicates a modified
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] FIG. 1 shows a diesel engine system for a vehicle having a
common rail type fuel injection system. FIG. 2 shows a control
system for the engine. The diesel engine system 1 has an engine 10,
an intake system 20, an exhaust system 30, a fuel injection device
40, an exhaust-gas recirculation (EGR) system 50, a forced
induction system 60 and a cooling system 70. The engine 1 is
controlled by an electric control system that has an engine control
unit (ECU) 80 such as a micro controller.
[0023] Referring to FIG. 1, the engine 10 is a 4-stroke
multi-cylinder engine having a plurality of combustion chambers 11.
The engine 10 has intake valves 12, exhaust valves 13 and a valve
driving system for driving the intake and exhaust valves. The
intake valves 12 allow and interrupt intake airflow into the
combustion chambers 11 respectively. The exhaust valves 13 control
exhaust-gas flow from the combustion chambers 11 to the exhaust
system 30. The valve driving system has an intake camshaft and an
exhaust camshaft which are driven by the engine 10.
[0024] The valve driving system further has a variable valve timing
device (VVT) 14. The VVT 14 varies at least an opening and closing
timings of the intake valves 12 in a delaying direction and an
advancing direction in accordance with a control signal from the
ECU 80. The VVT 14 varies rotational phase difference between a
driving shaft (crankshaft) and the intake camshaft and the exhaust
camshaft.
[0025] The intake system 20 has an intake pipe 21, an intake
manifold 22 and an intake throttle valve 23. The intake pipe 21 is
connected with an air cleaner. The forced induction system 60 is
disposed on the intake pipe 21. The intake pipe 21 is connected to
the intake manifold 22 that branches to the combustion chambers 11.
The intake pipe 21 has the intake throttle valve 23 downstream the
forced induction system 60. The intake throttle valve 23 has a
driving device 231 such as a motor and a valve 232 driven by the
driving device 231. The valve 232 varies an opening degree of the
intake pipe 21 to control an amount of airflow. The driving device
231 is connected to the ECU 80 and drives the valve 232. An intake
intercooler 24 is disposed on the intake pipe 21 between the forced
induction system 60 and the intake throttle valve 23. The intake
intercooler 24 cools an intake air.
[0026] The exhaust system 30 has an exhaust pipe 31, and an exhaust
manifold 32. The exhaust pipe 31 leads the exhaust gas to a
catalyst converter and a silencer. The forced induction system 60
is disposed in the exhaust pipe 31. The exhaust manifold 32
connects the exhaust pipe 31 and the combustion chambers 11.
[0027] The fuel injection system 40 has a fuel injection pump 41, a
common rail 42 and injectors 43. The fuel injection pump 41
pressurizes fuel from a fuel tank and supplies the pressurized fuel
to the common rail 42. The common rail 42 accumulates fuel
pressurized in a predetermined pressure. The injectors 43 are
connected with the common rail 42 and receive the pressurized fuel
from the common rail 42. Each of the injectors 43 has an
electromagnetic valve 431 connected with the ECU 80. The
electromagnetic valve 431 controls fuel injection in response to a
control signal from the ECU 80. Therefore, the ECU 80 can control
an amount of fuel injection and timing for injecting fuel with
respect to a crank angle of the engine 10.
[0028] The EGR system 50 has an EGR pipe 51 and an EGR valve 52.
The EGR pipe 51 connects the exhaust pipe 31 and the intake pipe
21. The EGR pipe 51 returns a part of the exhaust gas as an EGR gas
into the intake air. The EGR valve 52 is disposed on the EGR pipe
51 for controlling an amount of the EGR gas flowing in the EGR pipe
51 in response to a control signal from the ECU 80.
[0029] The forced induction system 60 is a variable turbocharger
such as a variable nozzle turbocharger that is capable of varying a
boost pressure. The turbocharger has an exhaust turbine 61, an
intake turbine 62 and a turbo actuator 63. The exhaust turbine 61
is disposed in the exhaust pipe 31 and is driven by the exhaust gas
flow. The intake turbine 62 is disposed in the intake pipe 21 and
driven by the exhaust turbine 61 for forced induction. The turbo
actuator 63 primarily varies a passage area formed between the
turbine blades of the exhaust turbine 61 and a turbine casing and
changes a boost pressure. The intake intercooler 24 cools the
intake air that may be heated by the intake turbine 62.
[0030] The cooling system 70 has an engine cooling part 71, an EGR
cooler 72, a radiator 73 and a water pump 74. The engine cooling
part 71 cools the engine 10. A conduit 701 is provided among the
engine cooling part 71, the radiator 73, and the water pump 74 to
form a closed loop of cooling water. A conduit 702 is provided to
form a branch passage to the EGR cooler 72. The EGR cooler 72 cools
the EGR gas flowing in the EGR pipe 51. The water pump 74 is
connected with the ECU 80 and activated or deactivated to control
cooling water flow in the conduits 701 and 702. Thus a cooling of
the EGR gas by the EGR cooler 72 is executed and stopped in
response to a control signal from the ECU 80. Alternatively, an
electromagnetic valve may be disposed in the conduits to control
the cooling water.
[0031] The ECU 80 is a micro controller having well known
configuration such as a CPU, RAM, and ROM. The ECU 80 is coupled
with sensors and actuators as shown in FIG. 2. A NE sensor 81
detects an engine speed NE. An accelerator sensor 82 detects an
operated position of an accelerator pedal. A temperature sensor 83
detects a temperature of cooling water in a water jacket of the
engine 10. A pressure sensor detects a fuel pressure in the common
rail 42. The ECU 80 is coupled with the electromagnetic valve 431
for the injector 43, the driving device 231 for the throttle valve
23, the EGR valve 52, the water pump 74, the VVT 14, and the turbo
actuator 63.
[0032] FIG. 3 shows a flowchart showing an operation of the ECU 80.
The engine 10 is usually operated under a certain amount of EGR,
and a predetermined delayed injection timing. Such a basic engine
control reduces a temperature during fuel combustion and reduces
the emissions of NOx and particulates. The ECU 80 determines engine
operating condition and engine load condition based on a detected
temperature Tw indicated by an output signal of the temperature
sensor 83 and a detected operated position of the accelerator pedal
indicated by an output signal of the accelerator sensor 82. The ECU
80 controls an operation of the EGR cooler 72 in an activated
condition or a deactivated condition in accordance with determined
engine load. The ECU 80 also controls a valve timing of the intake
valve 12 via the VVT 14 in accordance with the determined engine
load. The ECU 80 further controls a boost pressure via the forced
induction system 60 in accordance with the determined engine
load.
[0033] At a step S100, the ECU 80 inputs the water temperature Tw
from the temperature sensor 83. The ECU 80 determines engine
operating condition in accordance with the water temperature Tw.
For instance, the ECU 80 determines that whether the engine 10 is
operated under a warming up period or the engine 10 is operated
after a completion of the warming up. In a step S101, the ECU 80
compares the detected temperature Tw with a predetermined threshold
temperature Tws. For example, the Tws is set 50.degree. C. If the
temperature Tw is higher than the threshold temperature Tws, the
ECU 80 determines that the engine 10 is operated after the
completion of the warming up. Otherwise, the ECU 80 determines that
the engine 10 is operated under the warming up operation, and
proceeds to a step S104. As a result, the step 101 inhibits the
other controls, especially steps S106-S108, when the engine is
operated under the warming up operation.
[0034] If the warming up is completed, the ECU 80 inputs the
operated position of the accelerator pedal in a step S102. In a
step S103, the ECU 80 determines the engine load based on the
operated position of the accelerator pedal. The engine load is
determined by looking up a map as shown in FIG. 4. In this
embodiment, the engine load is obtained as three ranges, a range of
low engine load, a range of medium engine load and a range of high
engine load.
[0035] If the ECU 80 determines that the engine 10 is operated
under the warming up operation, or determines that the engine 10 is
operated under the low engine load, the ECU 80 executes a step
S104. In the step S104, the ECU 40 deactivates the water pump 74 to
stop a cooling operation of the engine 10 and the EGR cooler 72.
Deactivating the EGR cooler 72 causes an increase in the
temperature of the intake air since the EGR gas is not cooled.
Therefore, it is possible to increase the compression end
temperature and to improve an ability of fuel ignition. The ECU 80
maintains the delayed injection timing during the warming up
operation and the low engine load.
[0036] FIG. 5 shows the temperature in the combustion chamber when
the engine is operated under the low engine load. A thick solid
line indicates this embodiment. A chain line indicates an ordinary
engine. A broken line indicates a technique disclosed in
JP-A-11-315739. A narrow solid line indicates an engine with low
theoretical compression ratio. Tp1, Tp2, Tp3 and Tp4 denote
compression end temperatures. Tm1, Tm2, Tm3 and Tm4 denote maximum
temperatures during combustion cycle. Tp1 of the embodiment is
almost the same as Tp2, and is much higher than Tp3 and Tp4.
Therefore, according to this embodiment, the fuel injected into the
combustion chamber is readily ignited. Additionally, since Tp1 is
higher than a lower limit for ignition and is sufficient to keep
the temperature above the lower limit, it is possible to keep the
delayed injection timing. As a result, according to the embodiment,
it is possible to decrease Tm1 and a combustion speed, and to
reduce the emissions of NOx and particulates.
[0037] On the contrary, Tp4 is too low to keep the temperature
above the lower limit. Therefore, the ignition becomes instable.
Moreover, Tm4 is not increased due to the instable ignition. Tp3 is
still low to ensure ignition. Therefore, JP-A-11-315739 advances
the injection timing to prevent the engine from ignition failure.
However, such the advanced injection timing causes an excess
increase of combustion temperature. For example, Tm3 may reach
close to Tm2. As a result, the emissions become worse.
[0038] If the ECU 80 determines that the engine 10 is operated
under the medium engine load in the step S103, the ECU 80 activates
the water pump 74 to execute cooling of the engine 10 and the EGR
cooler 72 in a step S105. The ECU 80 maintains the delayed
injection timing during the medium engine load. Therefore, the
temperature of the EGR gas is decreased, and the temperature of the
intake air is not increased even the engine 10 is operated under
the medium engine load. As a result, it is possible to reduce the
emissions.
[0039] If the ECU 80 determines that the engine 10 is operated
under the high engine load in the step S103, the routine branches
to a step S106. In the step S106, the ECU 80 activates the water
pump 74. In a step S107, the ECU 80 delays a closing timing of the
intake valve 12 by controlling the VVT 14. In a step S108, the ECU
80 increases a boost pressure of the forced induction system 60.
The ECU 80 maintains the delayed injection timing during the high
engine load.
[0040] In the high engine load, the EGR cooler 72 cools the EGR gas
to decrease the intake air temperature. However, in the high engine
load, an amount of heat generated by combustion is increased due to
an increased amount of fuel corresponding to a relatively wider
opening degree of the accelerator pedal and throttle valve. In
order to avoid rising temperature in the combustion chamber, the
ECU 80 adjusts the closing timing of the intake valve 12. By
delaying the closing timing of the intake valve 12, the actual
compression ratio is decreased due to a decrease of effective
compression stroke of the engine 10. Therefore, the delayed closing
timing of the intake valve 12 also works as a means for decreasing
the compression end temperature. However, the delayed closing
timing of the intake valve 12 also decreases the heat capacity in
the combustion chamber 11, and results in an increase of the
maximum combustion temperature. In order to decrease the maximum
combustion temperature, the ECU 80 adjusts an amount of intake air
induced into the combustion chamber 11. The ECU 80 drives the turbo
actuator 63 in a direction to increase the boost pressure so that
the amount of the intake air induced into the combustion chamber 11
is increased. As a result, according to the embodiment, it is
possible to decrease the compression end temperature and the
maximum combustion temperature even in the high engine load.
[0041] FIG. 6 shows the temperature in the combustion chamber when
the engine is operated under the high engine load. A thick solid
line indicates this embodiment. A chain line indicates an ordinary
engine. A broken line indicates a conventional technique disclosed
in JP-A-11-315739. Referring to FIG. 6, Tp3 and Tm3 are lower than
Tp2 and Tm2 respectively. The conventional technique may decrease
both of the compression end temperature and the combustion maximum
temperature from the ordinary engine. However, the decreased
temperatures are not sufficient to reduce the emissions. Tp1 and
Tm1 are lower than Tp2, Tp3, Tm2 and Tm3 respectively. The
embodiment provides further decrease in the temperatures.
Therefore, it is possible to reduce the emissions in the high
engine load.
[0042] The above described advantages in the high engine load are
obtained under the following conditions. (1) The engine speed NE of
the engine 10 after completion of the warming up operation is set
2600 r.p.m (revolution per minute). (2) The engine load is set 50%.
(3) The delayed closing timing of the intake valve 12 is set ABDC
(After Bottom Dead Center) 50.degree. CA (Crank Angle). A normal
closing timing of the intake valve 12 is set ABDC 30.degree. CA.
(4) The boost pressure is set 210 kPa when the closing timing of
the intake valve is delayed. The boost pressure is set 154 kPa when
the closing timing of the intake valve is not delayed. (5) An EGR
ratio is set 30%. (6) The injection timing is set BTDC (Before Top
Dead Center) 1.degree. CA.
[0043] In the embodiment, the EGR cooler 72 works as means for
adjusting the intake air temperature. The VVT 14 works as means for
adjusting an actual compression ratio. The forced induction system
60 works as means for adjusting an amount of intake air effectively
induced into the combustion chamber. The ECU 80 controls the system
so that the engine 10 is operated under a relatively high ratio of
the EGR amount and the delayed injection timing. Therefore, the EGR
system 70 works as means for decreasing the compression end
temperature and the maximum combustion temperature. The injection
system 40 for the delayed injection timing works as means for
decreasing the maximum combustion temperature. The ECU 80 further
controls the system when the engine 10 is operated under the
relatively high EGR ratio and the delayed injection timing so that
the intake air temperature is decreased as the engine load is
increased, the actual compression ratio is decreased as the engine
load is increased, and the amount of intake air induced into the
combustion chamber is increased as the engine load is increased. As
a result, it is possible to provide the system that is capable of
stabilizing ignition of fuel in the low engine load and the engine
starting, and reducing the emissions of NOx and particulates
regardless of the engine load.
[0044] In the embodiment, although, the EGR system with the EGR
cooler 72 is used for decreasing the compression end temperature,
the present invention may be applied to a system that has no EGR
system. In such a modification, the steps S104, S105, and S106 are
removed from the control processing of the ECU 80. The ECU 80
controls the forced induction system 60 so that the boost pressure
is increased in accordance with an increase of the engine speed NE
and an increase of engine load. Such a forced induction
characteristic improves fuel economy and the emissions. FIG. 7
shows the boost pressure with respect to the engine load. Although
the forced induction system 60 has a capacity higher than an upper
limit as shown in FIG. 7, in a normal condition, the boost pressure
is limited below the upper limit in order to protect the engine 10.
In the modification, the engine load is determined based on the
operated position of the accelerator pedal.
[0045] The ECU 80 executes the step S107 and S108 when the engine
load is in the range of the high engine load. In the step S108, the
ECU 80 allows that the boost pressure exceeds the upper limit.
According to this modification, the compression end temperature can
be decreased due to a decrease of the actual compression ratio
obtained by delaying the closing timing of the intake valve 12.
Further, the maximum combustion temperature can be decreased due to
an increase of the amount of intake air obtained by increasing the
boost pressure. In the modification, the intercooler 24 also works
to decrease the intake air temperature that may be heated by the
forced induction system 60. Therefore, the intercooler 24 may works
as the EGR cooler 72 for decreasing intake air temperature as the
engine load is increased.
[0046] Further, the present invention may apply to a gasoline
engine.
[0047] Although the present invention has been described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications will be apparent to those skilled in the art.
Such changes and modifications are to be understood as being
included within the scope of the present invention as defined in
the appended claims.
* * * * *